1. Field of the Invention
The present invention relates to a sustained-release preparation which releases a physiologically active substance over a period of at least about 5 months.
2. Description of Related Art
A microsphere-type sustained-release preparation of drugs containing a biodegradable polymer is described in JP-A 118512/1982 (EP-A 52510), 150609/1982 (EP-A 58481), 100516/1985 (EP-A 145240), 201816/1987 (EP-A 190833), 321622/1992 (EP-A 442671) and 97334/1995 (EP-A 601799), for instance. Especially in JP-A 100516/1985 (EP-A 145240) and 201816/1987 (EP-A 190833), production of sustained-release microcapsules of a water-soluble drug with good dispersibility and high entrapment ratio by an in-water drying method is described. In JP-A 321622/1992 (EP-A 442671), long-term sustained-release microcapsules designed for zero order release of a polypeptide over a period of at least 2 months and containing a copolymer or homopolymer having a lactic acid/glycolic acid ratio of 80/20 to 100/0 and having a weight-average molecular weight of 7,000 to 30,000 are described.